The recording density of magnetic tapes is ever increasing. With increased recording density, magnetic tapes have the capability to hold an ever increasing amount of information on the same length of tape. While original tapes may have had only a few tracks, modern tapes can have, for example, thirty-two tracks.
This increased capacity comes at a cost, however. Heavy system noise, residual interference and severe nonlinear distortions can become aggravated in read/write channels. Conventional error correction coding (ECC) may have difficulty handling these problems and system performance may be impaired.
One of the conventional problems with high density recording systems are dropouts. These dropouts are commonly seen in magnetic tape recording channels. They may cause significant signal amplitude loss and excessive amounts of peak shift. As the amplitude of the signal decreases significantly, it can be difficult to read/extract/write the data from/to the high density tape. Dropouts may be one of the major reasons for block errors at low SNR in high density tape recording.
Also major limiting factors include cycle slip and failure of timing recovery systems. These limiting factors can affect the performance of read/write channels as they can cause long bursts of bit errors. Cycle slip occurs when a clock gets out of synchronization with the data. This may cause part or all of the bits in a data sector to be in error until the end of the data sector. It prevents reasonable block error rate at high recording densities.
To ensure that high density magnetic recording systems continue to work reliably at significantly degraded signal to noise ratios (SNR), iterative soft coding techniques have been introduced.
At least one of these iterative soft coding techniques that shows promise in handling these problems is low density parity check (LDPC) coding. Simulation results and theoretic analysis demonstrate that the error correcting performance of LDPC codes is extremely close to the Shannon Capacity, the theoretical maximum error correction capability.
LDPC coding can be very beneficial to the high density magnetic tape recording products. But, incorporating LDPC encoder/decoder into each of the 32 tape read/write channels may be very expensive. In addition, dropouts, cycle slips and failures of timing recovery are big hurdles that may prevent reliable performances of tape products.
Encoder/decoder designs of LDPC codes can be very intricate and the hardware implementations of LDPC encoders/decoders may require a significant amount of hardware resources (gates, memory, etc.). This may be especially true when thirty-two or more copies of LDPC encoders/decoders are used for the thirty-two tracks of magnetic tape recording systems, such as in a system recording/decoding a thirty-two track tape.
In a first illustrative embodiment, an LDPC coding system includes a number of LDPC encoders. The total number of LDPC encoders is between one and one fewer than the total number of tracks on a high density tape to which data blocks are to be written (i.e., for a thirty-two track system, the total number of encoders would be between one and thirty-one).
Also, in this illustrative embodiment, a number of LDPC decoders between one and one fewer than the total number of tracks on the high density tape are provided.
This illustrative embodiment also includes a plurality of read/write heads corresponding to the number of tracks on the high density tape to which data blocks are to be written. For example, on a thirty-two track tape, there are thirty two read/write heads.
In this illustrative embodiment, the system also includes at least one multiplexer in operable communication with the LDPC encoders to transfer data blocks from each of the encoders to an appropriate read/write head, and at least one de-multiplexer in operable communication with the LDPC decoders to transfer data blocks from each of the appropriate read/write heads to an appropriate decoder.
According to this illustrative embodiment, the LDPC encoders are operable to break data from an incoming data sector into the data blocks to be written to the high density tape. In this embodiment each data block is of equal size to the other data blocks. The total number of data blocks each sector is broken into are equal to the total number of tracks divided by the number of encoders.
Finally, in this illustrative embodiment, the LDPC decoders are operable to assemble the data blocks into data sectors. A number of data blocks equal to the total number of tracks divided by the number of decoders is assembled into a single data sector.
In a second illustrative embodiment, an LDPC encoding apparatus includes one or more LDPC encoders. The total number of LDPC encoders is no more than one less than a total number of tracks on a high density tape to which data blocks are to be written.
In this embodiment, one or more multiplexers are in communication with the one or more LDPC encoders and are operable to transmit data from the one or more LDPC encoders to each of a plurality of read/write heads. Each of the read/write heads corresponds to a track on the high density tape to which data blocks are to be written.
In this embodiment, the LDPC encoders are operable to break a data sector into a number of blocks of equal length. The number of data blocks corresponds to the total number of tracks on the high density tape divided by the number of LDPC encoders. The LDPC encoders are further operable to provide each of the data blocks with one or more fundamental identifying pieces that identify the data block for reassembly.
In still a third illustrative embodiment, a method of writing to a high-density tape includes breaking incoming data sectors into data blocks of equal length using a fewer number of LDPC encoders than there are tracks on the high density tape. The method also includes providing each data block with identifying information that at least identifies a tape track to which the data block is to be written. Each data block is written to a different tape track in this embodiment.
The method includes routing each data block to the tape track to which the data block is to be written. Finally, the method includes writing each data block to the tape track to which the data block is to be written.
In a fourth illustrative embodiment, a method of reading from a high-density tape includes reading data blocks from individual tracks on a high density tape. In this method, each data block including identifying information that at least identifies a reassembly order for the data blocks.
The method further includes combining the data blocks into at least one data stream based at least in part on the identifying information.
In this embodiment, the method also includes feeding the at least one data stream into one or more LDPC decoders, the number of LDPC decoders being between one and one fewer than the total number of tracks on the high density tape.
Finally, the method includes recombining the data blocks into usable data sectors using the LDPC decoders.